Have you tried the Google Play Music Chrome app instead of the standalone music manager desktop application?

I use the Music Manager, too, since I can load it manually (instead of letting it start automatically at boot) and unload it (Quit from the systray icon) and I'm kind of obsessive about the lean/mean machine thing.

But maybe the Chrome app would work better for you.

On the 20 thousand track limitation, I don't think the playlist trick would work,  even if it, you know, worked... er, that is to say, I think there's basically a 20k  title limit that you can't get past. 

Me, I'm an All Access subscriber, so my personal music locker is really only used for stuff that isn't available via subscription streaming.  (Happily, 'favoriting' tracks from AA into your library doesn't eat into the 20k upload track limit.)

I have a couple of playlists of recent music in the genres I'm currently listening to. I'd like to sync this with Play and I'd be well within the limit. I kind of get round this by sorting the sub-directories by recently modified and then dropping a couple of columns of them onto the Music Manager.

The real issue is that Manager assumes you use iTunes and grudgingly Windows Media Player. If you stay well away from both those or use a platform that doesn't support them, you're screwed. .pls and .m3u have been around for a long while now so there's really no excuse for not supporting them.

The Chrome App helps if you're using a Chromebook, but Chromebooks are rubbish if you have a large music collection anyway. Not least because they can't support a home NAS or network shares.

Collecting Music? I must be a dinosaur!

LOL... you're not really alone on the collecting front --  I've got 1200 LPs, 500 CDs, 200 singles and something like 19k 128 and 192 kbps tracks I bought through the old-old Emusic store (when it was all-you-could-DL for $15 a month; those were the days my friend, mostly old catalog the labels assumed no one wanted, but since I'm into old jazz, folk, blues, real country, classical,  etc, it was mostly right up my alley; that said, with subscription streaming, I have access to almost everything, new or old, these days -- and I like the fact that the artists/labels get paid with each play, unlike playing from files on my computer or from CD).

Anyhow, I actually don't use iTunes or WMP, myself, probably two of the very least likely standalones I'd use. (I use Foobar to play local files.)

But because I'm so deeply into the stream subscription thing, the GPM system, allowing me to mix subscription streams with stuff from my personal music locker ends up working out really well for me.

+Julian Bond Have you tried combining albums into single mp3s?  Google will let us upload mp3s up to 300mb in size.  I do that for albums that are best listened to as entire albums.  Gives me that much more room to squeeze the most out of my locker.  :)